Rhodes Chroma Polaris

Dear Dave and Paul,

Yes, my Polaris will hold all patches and settings while the main power is on. Where I checked the battery voltage was simply at the connector to the main board. I was not sure which pin on the RAM chips would be the best to check the voltage when the main power is off. I can check that now that I know which pins are used. 
I looked online and the IN34A germanium diode is easy to find. So I will get one and replace it. 
Thank you both for the advice.
Once I change out the diode, I report back.Hope that is all it is!

Sincerely,

Brett


--- In chromapolaris@yahoogroups.com, "Paul D. DeRocco"  wrote:
>
> > From: David Clarke
> > 
> > Brett - the batteries are going to be used to power the RAM, but only 
> > when the unit is shut off.
> > 
> > When main power is applied to the unit, the RAM will be 
> > powered by the 
> > on-board power supply.
> > 
> > If the Polaris is fully functional when it is powered up (e.g., if 
> > you're able to save patches, recall patches, etc.) then you can be 
> > reasonably confident that the RAM itself is fine.
> > 
> > When power goes away, (and when it comes up) there is a 
> > circuit on-board 
> > that switches the CMOS RAM power to/from the battery.  This 
> > is shown in 
> > the "Battery Back Up Power Supply" circuit in the schematics:
> > 
> > http://www.rhodeschroma.com/content/polarisservicemanual/polar
> > isserviceschematics/computermemorydatapanelbuffersbattery.pdf
> > 
> > If the problems only occur across a power-cycle, then the most likely 
> > implication is that there's something not quite right with 
> > regard to the 
> > operation of that circuit.
> > 
> > > I have new D-cell batteries in and I check with a
> > > voltmeter that indeed 3.1V is getting to the main board when
> > > the power is off.
> > 
> > It's not exactly clear from this note where the voltage was 
> > measured - 
> > but you'll want to measure it at the +5V Batt location on the 
> > CMOS RAM 
> > chips themselves (e.g., pin 26 or 28 of those devices) to 
> > confirm that 
> > it is making it to where it is needed.
> > 
> > If it is there, you'll want to watch that voltage location with an 
> > 'scope to confirm that during the power on/power off the 
> > voltage doesn't 
> > glitch low.
> > 
> > If it isn't there, then it's just a matter of tracing back to 
> > find where 
> > where the battery volage is 'lost' from the batteries (e.g., CR1 bad).
> > 
> > Good luck, and let us know how you make out,
> 
> CR1 is the most likely culprit. If anything even momentarily shorts the
> memory power line to ground, that will blow out. That could be diagnosed
> easily enough with a meter. If it's bad, it should be replaced with either
> an equivalent germanium diode, or perhaps a Schottky diode. A regular
> silicon diode can be used in a pinch, but will not tolerate as low a battery
> voltage before the RAMs lose their data.
> 
> -- 
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco@...
>